1. Field of the Invention
In audio signal quality detectors and the like utilized, for example, in voting or receiver selecting systems, it is necessary to determine which receiver of a plurality of receivers is providing the best signal, i.e. which receiver is receiving the strongest or best quality of signal. It is well known that the discriminator in an FM receiver provides a noise signal that is inversely proportional to the strength or quality of the signal being received. Thus, if the noise level at the output of the discriminator can be determined, the receiver receiving the strongest or best quality of signal can be determined also. To determine the noise level, the output of the discriminator must be constantly monitored to select valleys in the audio signal and determine the noise level in the valley.
2. Description of the Prior Art
U.S. Pat. No. 3,729,682, entitled "Audio Signal Quality Indicating Circuit", issued Apr. 24, 1973, discloses a prior art system wherein an inverted peak detector having a relatively long time constant is utilized as a valley detector to constantly monitor valleys in the envelope of the audio signal from a discriminator. Because this prior art valley detector has a flat attack and slow decay, when a good signal suddenly fades deeply, the system is not capable of quickly switching to another receiver.